Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$176.88	12.695%	$199.3349	$199.33	$199.35	$199.30
Purchase #2	$91.81	12.852%	$103.6094	$103.61	$103.60	$103.60
Purchase #3	$119.48	6.551%	$127.3071	$127.31	$127.30	$127.30
Purchase #4	$64.85	3.207%	$66.9297	$66.93	$66.95	$66.90
Purchase #5	$51.42	13.455%	$58.3386	$58.34	$58.35	$58.30
Purchase #6	$16.70	9.542%	$18.2935	$18.29	$18.30	$18.30
Purchase #7	$86.60	4.830%	$90.7828	$90.78	$90.80	$90.80
7 purchase totals =	$607.74		$664.5960	$664.59	$664.65	$664.50